Bacterial decontamination of water by means of pulsed corona discharges

Abstract

Summary form only given. Whereas bacterial decontamination of gases by means of pulsed corona discharges is now a firmly established method, efforts to use pulsed corona or streamer discharges in liquids for decontamination have only begun recently. This is due to the extremely high electric fields intensities required to initiate plasma formation in liquids. Using a wire anode and a planar cathode, experimental studies have shown that electric field intensities of approximately 2.5 MV/cm at the wire surface are needed to obtain pulsed corona discharges in tap water. By using a tungsten wire with 75 /spl mu/m diameter, two cm apart from a plane cathode, and applying a 600 ns, 135 kV square wave pulse, we were able to obtain a water corona discharge (PWC) without glow-to-arc transition. The effect of these discharges on bacteria was studied using water contaminated with Escherichia coli and Bacillus subtilis, the latter in both the vegetative and spore state. The strongest effect was obtained on E. coli. The concentration of E. coli could be reduced by two orders of magnitude after applying 3 corona discharges to the water. The corresponding energy expenditure is 4 J/ml. The decontamination rate had the largest values at the beginning, and decreased considerably after 15 electrical discharges, an effect which has also been observed in experiments using pulsed electric fields (PEF), and is assumed to be due to bacterial cell adhesion to and release from the chamber walls. For B. subtilis in the vegetative state, it took 20 discharges to reach the same result, corresponding to an energy expenditure of 28 J/ml. There was no effect on B. subtilis spores. Comparisons with the PEF method, a widely explored electro-technology used for bacterial decontamination, indicate that the decontamination efficiency of the PWC method is slightly higher than that of the PEF method.